Method for charging a battery by near-field communication

ABSTRACT

The subject matter of the present invention is a method for charging a power supply battery of a portable device by means of near-field communication with a base station. The method, implemented by the device, comprises, the primary antenna of the base station and the secondary antenna of the device being electromagnetically coupled, the steps of modifying (E 1 ) the coupling between the primary antenna of the base station and the secondary antenna of the device, of receiving (E 3 ) an authentication request signal sent by the base station subsequent to said step of modifying the coupling, and of charging (E 4 ) the power supply battery of the device from the energy of the received authentication request signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase Application of PCTInternational Application No. PCT/EP2018/050035, filed Jan. 8, 2018,which claims priority to French Patent Application No. 1750345, filedJan. 17, 2017, the contents of such applications being incorporated byreference herein.

FIELD OF THE INVENTION

The present invention relates to the field of charging power supplybatteries and relates more particularly to a method for charging a powersupply battery of a portable device by means of near-field communicationand to a portable near-field communication device. The invention isparticularly applicable to the fast charging of batteries of small sizefitted to portable devices such as contactless access badges, hands-freekits for telephone calls, Bluetooth® earpieces, etc.

BACKGROUND OF THE INVENTION

In a known manner, the passenger compartment of a motor vehicle may beaccessed or the motor/engine of a motor vehicle may be started via anear-field communication (NFC) wireless communication system. Such asystem comprises a detector mounted inside the vehicle, taking the formof a base station comprising what is referred to as a “primary” antenna,and a portable device comprising what is referred to as a “secondary”antenna, both of which are compatible with NFC technology. The devicemay for example take the form of an electronic tag, of a card, of abadge, of a box, etc.

To detect a compatible device, the base station emits an interrogationsignal periodically, for example every 100 ms, and for a very shortduration, for example 30 μs, so as to save energy, which interrogationsignal generates an electromagnetic field in proximity to the primaryantenna.

Thus, when a compatible device is placed in proximity to the basestation, it modifies the electromagnetic field generated while theinterrogation signal is being emitted, thereby forming a couplingbetween the primary antenna of the base station and the secondaryantenna of the device. This coupling, which modifies the intensity ofthe current flowing through the primary antenna, is detected by the basestation, which thus deduces therefrom that a device is in proximity.

Once a device has been detected, the base station emits anauthentication request signal between two emissions of the interrogationsignal, the periodic emission of the interrogation signal providing theassurance that the coupling is still in place and that the device istherefore still present in proximity to the base station. Thisauthentication request signal includes a request to authenticate thedevice, which in turn responds to the base station by sending a responsesignal including its identifier.

If the identifier of the device is valid, the base station authorizesthe unlocking of the passenger compartment or the starting of themotor/engine of the vehicle. If the device is removed, the couplingbetween the primary antenna and the secondary antenna is broken and anyand all communication between the device and the base station isinterrupted until a new coupling is detected.

The portable device may be passive, in which case it lacks a powersupply battery, or else active or semi-active, in which case it includesa power supply battery.

In the case of an active or semi-active device, when the battery isempty, it is necessary for it either to be switched out or to becharged, or for the device to be replaced. Since switching out thebattery, and especially the device, may prove to be very expensive,charging is usually preferred by far.

Such a charging operation may be carried out by connecting the device toan electrical network via a power supply cable, which may prove to belaborious, or by placing it on a wireless induction charging module,which is easier to use, as long as the device is compatible. Such aninduction charging module may however prove to be very expensive, inparticular when its capacity for fast-charging a portable device issubstantial.

SUMMARY OF THE INVENTION

An aspect of the invention aims to overcome these drawbacks at leastpartly by providing a simple and effective solution for charging a powersupply battery of a portable near-field communication device from a basestation, in particular in a motor vehicle.

In particular, an aspect of the invention aims to allow the fastcharging of active or semi-active batteries of small size, for examplefitted to access cards, hands-free telephone kits, Bluetooth® earpieces,etc.

To this end, an aspect of the invention first relates to a method forcharging a power supply battery of an active or semi-active portabledevice by means of near-field communication with a base station, saidbase station comprising what is referred to as a “primary” antenna, saiddevice comprising what is referred to as a “secondary” antenna.

The method, implemented by the device, is noteworthy in that itcomprises, the primary antenna of the base station and the secondaryantenna of the device being electromagnetically coupled, the steps ofmodifying the coupling between the primary antenna of the base stationand the secondary antenna of the device, of receiving an authenticationrequest signal sent by the base station subsequent to said step ofmodifying the coupling, and of charging the power supply battery of thedevice from the energy of said received authentication request signal.

The method according to an aspect of the invention advantageously allowsa base station suitable for near-field communication to be used tocharge the battery of active or semi-active near-field communicationdevices. The base station may for example be mounted inside a vehicle orelse be a smartphone or any other suitable near-field communicationdevice. With the method according to an aspect of the invention, thedevice modifies the coupling between the device and the base station soas to cause the base station to emit at least one new authenticationrequest signal, preferably a plurality of authentication requestsignals, for the purpose of charging the power supply battery of thedevice. The modification of the coupling, and consequently the chargingof the battery, may thus be carried out rapidly, either until thebattery is charged or the coupling between the device and the basestation is interrupted. Moreover, the method according to an aspect ofthe invention allows costs to be decreased with respect to an inductioncharging solution by virtue of the use of a near-field communicationbase station that is already present, obviating the need to provide amore expensive, dedicated charging station.

It should be noted that a more obvious solution would have been to usethe interrogation signals emitted periodically by the base station tocharge the battery of the active or semi-active device by induction.However, as mentioned above, since these signals are emitted by the basestation periodically, for example every 100 ms, and for a shortduration, for example 30 μs, so as to save energy, their energy densityis low. This would then result in it taking a substantial length of timeto charge the battery, for example at least three hours and potentiallyup to 20 hours depending on the duration and the period of the detectionpulses and the type of battery.

According to one aspect of the invention, the method comprises apreliminary step of electromagnetic coupling between the primary antennaof the base station and the secondary antenna of the device. This stepallows the primary antenna and the secondary antenna to be initiallycoupled so that the device may subsequently modify the coupling thereofand thus allow the power supply battery to be charged.

Preferably, the method comprises a step of detecting the time of the endof receiving the authentication request signal, the coupling then beingmodified as soon as the time of the end of receiving the authenticationrequest signal has been detected. This advantageously allows the batteryto be charged almost continuously, the authentication request signalsthen being received one after another.

In one embodiment, the coupling is modified periodically, preferablyevery 500 ms at the latest, so as to result in an authentication requestsignal being emitted systematically.

An aspect of the invention also relates to a device, preferably aportable, active or semi-active device, for near-field communicationwith a base station, said base station comprising what is referred to asa “primary” antenna, said device comprising a power supply battery andwhat is referred to as a “secondary” antenna that is capable of beingelectromagnetically coupled with said primary antenna, the device beingnoteworthy in that it comprises means for charging the power supplybattery from the energy of an authentication request signal emitted bythe primary antenna and received via the secondary antenna, and meansfor modifying a coupling between the primary antenna and the secondaryantenna.

In one advantageous embodiment, the device is an authentication devicefor activating a function of a motor vehicle such as, for example,unlocking access to the passenger compartment or starting themotor/engine of the vehicle.

Preferably, the means for modifying the coupling comprise a switchingbranch including a capacitor that is connected in parallel with aswitch.

Advantageously, the means for modifying the coupling comprise means forswitching said switch.

Preferably, the means for modifying the coupling are capable ofdetecting the time of the end of receiving the authentication requestsignal and of modifying the coupling as soon as said time of the end ofreceiving the authentication request has been detected.

As a variant or in addition, the means for modifying the coupling may becapable of modifying the coupling periodically such that a base stationlocated in the near field periodically emits an authentication signalallowing the power supply battery of the portable device to be charged.

According to one aspect of the invention, the device is furtherconfigured to authorize the charging of the power supply battery untilsaid power supply battery is fully charged or until the coupling betweenthe device and the base station is interrupted.

According to another aspect of the invention, the device is furtherconfigured to detect whether the power supply battery is fully chargedand, if so, to cease any and all modification of the coupling via themodifying means once the battery is fully charged.

Lastly, an aspect of the invention relates to a system for charging thepower supply battery of a portable near-field communication device, saidsystem comprising a device such as presented above and a base stationcomprising what is referred to as a “primary” antenna that is capable ofbeing electromagnetically coupled with the secondary antenna of saiddevice, said base station being configured to emit, via said primaryantenna, at least one interrogation signal, to detect a (new) couplingwith the secondary antenna of the device or a variation in an existingcoupling with the secondary antenna of the device, and to emit, via theprimary antenna, an authentication request signal when a coupling withthe secondary antenna has been achieved or once a modification to thecoupling with the secondary antenna has been detected.

Preferably, the base station is mounted inside a motor vehicle.

Advantageously, the base station may be a mobile telephone, for examplea smartphone, that is capable of near-field communication (NFC) with adevice for the purpose of charging the battery thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of aspects of the invention will becomeapparent from the following description provided with reference to theappended figures that are given by way of non-limiting example and inwhich identical references are given to similar objects.

FIG. 1 schematically illustrates one embodiment of the system accordingto an aspect of the invention.

FIG. 2 schematically illustrates one embodiment of the method accordingto an aspect of the invention.

FIG. 3 is an exemplary graphical representation of the periodic emissionof interrogation signals by the primary antenna of a base station in theabsence of coupling with a device.

FIG. 4 is an exemplary graphical representation of the emission ofinterrogation signals in alternation with the emission of authenticationrequest signals by the primary antenna of a base station of the systemof FIG. 1.

FIG. 5 is an exemplary graphical representation of the clock signals ofa flip-flop for switching the device of the system of FIG. 1.

FIG. 6 is an exemplary graphical representation of the state of theswitch of the device of the system of FIG. 1 when it is controlled bythe clock signals illustrated in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The system according to an aspect of the invention allows a power supplybattery of a portable device to be charged by a base station through theuse of near-field communication technology.

The term “near-field communication” is understood to mean thatcommunication is carried out by radio communication over a shortdistance, for example a few centimeters. In the context of this aspectof the invention, such near-field communication technologies grouptogether in particular RFID (radiofrequency identification) technologiesand the NFC standard or any similar technology.

An aspect of the present invention targets in particular active orsemi-active devices such as RFID access badges, for example foraccessing the passenger compartment of a motor vehicle, hands-free kitsfor mobile telephones such as for example Bluetooth® or BLE (Bluetooth®Low Energy) earpieces, but also any type of near-field communicationdevice, such as for example a smartphone, the battery of which needs tobe recharged by near-field communication.

In the non-limiting example described below, the base station is mountedinside a motor vehicle. It should be noted however that an aspect of theinvention relates more generally to the charging of a power supplybattery of a portable device by means of any type of base station usingnear-field communication technology, and which is not necessarilymounted inside a vehicle. It should be noted in particular that the basestation may be a smartphone or any other near-field communicationdevice.

FIG. 1 schematically shows one embodiment of the system 1 according toan aspect of the invention.

The near-field communication system 1 comprises a portable device 10 anda base station 20.

The portable device 10 is what is referred to as an “active” or“semi-active” near-field communication device, i.e. it comprises a powersupply battery BAT for supplying electricity. In this case in point, thepower supply battery is capable of being charged as will be describedbelow.

To allow communication between the device 10 and the base station 20,the base station 20 comprises what is referred to as a “primary” antennaLP and the device 10 comprises what is referred to as a “secondary”antenna LS, both of which are capable of being electromagneticallycoupled with one another and of emitting and receiving various types ofsignals, for example at the frequency of 13.56 MHz. In this example, theprimary antenna LP of the base station 20 and the secondary antenna LSof the device 10 both take the form of an inductive coil.

To detect the device 10, the base station 20 is configured to emit, viathe primary antenna LP, an interrogation signal periodically, forexample every 100 ms, and for a very short duration, for example 30 μs,so as to save energy, the emission of which interrogation signalgenerates an electromagnetic field in proximity to said primary antennaLP.

When the secondary antenna LS of the device 10 is immersed in anelectromagnetic field generated by the primary antenna LP of the basestation 20 during the emission of an interrogation signal, couplingtakes place between said secondary antenna LS and said primary antennaLP.

The base station 20 comprises a control module 200 that is configured toperform a plurality of tasks.

First, the control module 200 is configured to detect a variation in theintensity of the current flowing through the primary antenna LP or inthe voltage across the terminals of the primary antenna LP, which aresynonymous with the establishment of a coupling or with the modificationof an existing coupling between the primary antenna LP of the basestation 20 and the secondary antenna LS of the device 10.

The control module 200 is further configured to send, to the device 10,a request signal after having detected a new coupling or a variation ina pre-existing coupling between its primary antenna LP and the secondaryantenna LS. The energy density of this authentication request signal issignificantly higher than the energy density of an interrogation signaland therefore allows the power supply battery BAT to be charged morequickly. The authentication request signal includes in particular arequest by the base station 20 for the device 10 to authenticate itself.

When it receives an authentication request signal, the device 10 isconfigured:

-   -   in what is referred to as a “communication” mode, to transmit a        response signal to the base station 20, this response signal        comprising at least the identifier of said device 10;    -   in what is referred to as a “charging” mode, to charge its power        supply battery using the energy of the authentication request        signal.

The control module 200 is also configured to receive a response signalemitted by the device 10 and to use it according to the particularapplication. Thus, for example, in the case of a motor vehicle, if theidentifier of the device 10 is valid, the base station 20 may beconfigured to authorize the unlocking of the passenger compartment orthe starting of the motor/engine of the vehicle.

Communication mode may be implemented first to authenticate the device10 then, next, the device 10 may switch to charging mode so as to allowits power supply battery BAT to be charged.

Switching between communication mode and charging mode may take placeautomatically, for example depending on the need to charge the powersupply battery BAT, or be activated manually by a user.

To allow its power supply battery BAT to be charged from the energy of areceived authentication request signal, the device 10 comprises meansfor charging said power supply battery BAT. In other words, the chargingmeans are configured to charge the power supply battery from the energyof an authentication request signal received from the primary antenna LPof the base station 20.

In the example of FIG. 1, the charging means comprise a rectifiercircuit D2 connected both to the power supply battery BAT and to a firstterminal B1 and a second terminal B2 of the secondary antenna LS,allowing the signal delivered by the secondary antenna LS to berectified in order to charge the power supply battery BAT. By way ofexample, this rectifier D2 may take the form of a diode bridge, knownper se.

According to an aspect of the invention, the device 10 further comprisesmeans for modifying the coupling between the secondary antenna of thedevice 10 and the primary antenna of a base station 20.

Preferably, the means for modifying the coupling are capable ofmodifying the coupling as soon as the time of the end of receiving anauthentication request signal received from the base station 20 has beendetected. Specifically, this allows the base station 20 to quicklydetect a modification of the coupling between its primary antenna LP andthe secondary antenna LS of the device 10 so as to emit a newauthentication request signal.

To this end, in the example of FIG. 1, the means for modifying thecoupling comprise a diode D1 that is connected both to the firstterminal B1 of the secondary antenna LS and to the input of a high-passfilter F1. The rectifier diode D1 allows a sinusoidal signal received bythe base station 20 to be transformed into a DC signal for charging thebattery BAT.

A decoupling capacitor C3 is connected between a ground M and themidpoint between the diode D1 and the high-pass filter F1 so as tofilter out the parasitic signals entering the coil constituting thesecondary antenna LS.

Still with reference to FIG. 1, the means for modifying the couplingnext comprise a switching branch including both a matching capacitor C2,connected in parallel with a switch, and means MC1 for switching saidswitch. In this non-limiting example, the switch consists of atransistor T1, for example an NPN or PNP transistor, the emitter and thecollector of which are connected, respectively, to one of the branchesof the capacitor C2.

The device 10 also comprises a matching capacitor C1, connected inseries between the first terminal of the secondary antenna LS and themidpoint between the capacitor C2 and the transistor T1, allowing thecoil constituting the secondary antenna LS to be matched to the desiredoperating frequency.

In the illustrated embodiment, the switching means MC1 take the form ofa JK flip-flop, known per se. As a variant, it should be noted that anyother suitable switching means could be used.

The clock of the JK flip-flop is connected to the output of thehigh-pass filter F1. The J and K terminals of the JK flip-flop areconnected to a supply voltage Vcc. In the case of a PNP transistor, thetransistor T1 is connected to the Q output of the JK flip-flop. In thecase of an NPN transistor, the transistor T1 is connected to theinverse, Q\ output of the JK flip-flop. In the example illustrated inFIG. 1, the transistor is a PNP transistor and the Q terminal of the JKflip-flop is connected to the base of the transistor T1.

Preferably, the device 10 may be configured to detect whether the powersupply battery BAT is fully charged such that the modifying means stopmodifying the coupling.

Preferably again, the device 10 may be configured to authorize thecharging of the power supply battery BAT until it is charged or untilthe coupling between the secondary antenna LS and the primary antenna LPis interrupted.

An aspect of the invention will now be described in terms of theimplementation thereof with reference to FIGS. 1 to 6.

In this exemplary application, the portable device 10 is an RFID badgeintended to be carried by a user to allow his or her authentication by abase station 20 mounted inside a motor vehicle in order for said basestation 20 to activate a function of the vehicle such as, for example,unlocking the passenger compartment or starting the motor/engine of thevehicle.

In a preliminary step E0, an electromagnetic coupling C is firstproduced between the primary antenna LP of the base station 20 and thesecondary antenna LS of the device 10.

FIG. 3 illustrates the periodic emission, by the base station 20, of aninterrogation signal SI0 in the absence of a device 10 in proximity(i.e. in the absence of coupling C). This interrogation signal SI0 isemitted for example every 100 ms and for a very short time, for example30 μs, so as to save energy, such an emission generating anelectromagnetic field in proximity to the primary antenna LP of the basestation 20.

With reference to FIG. 4, when the device 10 is placed in proximity tothe base station 20, for example less than 10 cm away, a coupling C isproduced between the primary antenna LP of the base station 20 and thesecondary antenna LS of the device 10 while the interrogation signal SI1is being emitted, which then modifies the intensity of the currentflowing through the primary antenna LP (for example by increasing ordecreasing its amplitude, for example).

The base station 20 then detects this coupling C and deduces therefromthat the device 10 is requesting communication with said base station20. The base station 20 then transmits, via the primary antenna LP, anauthentication request signal SR1 to the device 10, which receives itvia its secondary antenna LS,

When the device 10 switches to charging mode so as to charge its powersupply battery BAT and according to an aspect of the invention, thedevice 10 will trigger the emission, by the base station 20, of aplurality of successive authentication request signals that it will useto charge the power supply battery BAT.

Thus, first, in a step E1, still with reference to FIG. 4, the device 10modifies the existing coupling C produced in step E0. More specifically,in step E1, the device 10 uses its switching means MC1 to modify theintensity of the current flowing through its secondary antenna LS andthus to modify the coupling C between said secondary antenna LS and theprimary antenna LP of the base station 20.

To achieve this, with reference to FIGS. 5 and 6, when the transistor T1is letting current through (i.e. the switch is closed), the capacitor C2is shorted (state A in FIG. 6) and the voltage across the terminals ofthe primary antenna LP is equal to the voltage across the terminals ofthe capacitor C1. This voltage allows the JK flip-flop to switch via itsclock H so as to control the transistor T1 so that it no longer allowscurrent through (switch open). In this case, the voltage across theterminals of the primary antenna varies and becomes equal to the sum ofthe voltage across the terminals of the capacitor C1 and of the voltageacross the terminals of the capacitor C2, which is then on (state B inFIG. 6). Modifying the coupling C by means of the device 10 modifies theintensity of the current flowing through the primary antenna LP of thebase station 20, which results in the amplitude of the interrogationsignal being modified, for example decreased for the interrogationsignal SI2 in the example of FIG. 4. Modifying the intensity of thecurrent flowing through the primary antenna LP modifies the currentflowing through the diode D1 and the filtering circuit F1 such that theclock signal of the JK flip-flop is modified once again. The JKflip-flop then once again switches the two-position switch (here thetransistor T1) to its closed position until the next emission of aninterrogation signal by the base station 20. Such a switching operationis thus performed each time the amplitude of the interrogation signalSI1, SI2 varies.

With reference to FIG. 4, modifying the coupling modifies theinterrogation signal SI2, which results in the intensity of the currentflowing through the primary antenna LP of the base station 20 beingmodified. The base station 20 perceives this modification as a newcoupling C (i.e. with a new device requesting to authenticate itself)and then triggers the emission of a new authentication request signalSR2 in a step E2.

This authentication request signal SR2 is received by the secondaryantenna LS of the device 10 in a step E3, which uses it to charge thepower supply battery BAT in a step E4.

The device 10 then detects, in a step E5, the time of the end ofreceiving the authentication request signal SR1 and then once againproceeds to modify the coupling C between the primary antenna LP and thesecondary antenna LS (step E1) during the emission of the nextinterrogation signal SI2 so as to receive a new authentication requestsignal SR2 and so on.

The successive authentication request signals are delivered to the powersupply battery BAT by the rectifier circuit D2 so as to charge itquickly.

The modification of the coupling C and hence the emission of requestsignals allowing the power supply battery BAT to be charged continuesfor as long as the device 10 chooses, for example until the power supplybattery BAT is fully charged or the device 10 is removed, interruptingthe coupling C.

The method according to an aspect of the invention thereforeadvantageously allows the emission of a plurality of successiveauthentication request signals to be triggered so as to quickly andeffectively charge the power supply battery BAT of the device 10. Themethod is particularly effective when it comes to charging batteries ofsmall capacity, delivering for example less than 2 W of power. Thebattery of an RFID access badge or of a Bluetooth® earpiece may thus beeasily and quickly charged in a few minutes.

1. A method for charging a power supply battery of a portable device bynear-field communication with a base station, said base stationcomprising a “primary” antenna, said device comprising a “secondary”antenna, said method, implemented by the device comprising:electromagnetically coupling the primary antenna of the base station andthe secondary antenna of the device; modifying the coupling between theprimary antenna of the base station and the secondary antenna of thedevice; receiving an authentication request signal sent by the basestation subsequent to the modifying of the coupling; and charging thepower supply battery of the device from the energy of said receivedauthentication request signal.
 2. The method as claimed in claim 1, themethod further comprising detecting a time of an end of receiving theauthentication request signal and wherein the coupling is modified assoon as the time of the end of receiving the authentication requestsignal has been detected.
 3. The method as claimed in claim 1, whereinthe coupling is modified periodically.
 4. The method as claimed in claim3, wherein the coupling is modified every 500 ms at the latest.
 5. Asystem for charging a power supply battery of a portable near-fieldcommunication device, said system comprising a device and a base stationcomprising a “primary” antenna that is capable of beingelectromagnetically coupled with a secondary antenna of said device,said base station being configured: to emit, via said primary antenna,at least one interrogation signal; to detect a coupling with thesecondary antenna of the device or a variation in an existing couplingwith the secondary antenna of the device; and to emit, via the primaryantenna, an authentication request signal when a coupling with thesecondary antenna has been achieved or once a modification to thecoupling with the secondary antenna has been detected.
 6. The system asclaimed in claim 5, wherein the device further comprising: means forcharging the power supply battery from energy of an authenticationrequest signal emitted by the primary antenna and received via thesecondary antenna; and means for modifying the coupling between theprimary antenna and the secondary antenna.
 7. The system as claimed inclaim 6, wherein the means for modifying the coupling comprise aswitching branch including a capacitor that is connected in parallelwith a switch.
 8. The system as claimed in claim 7, wherein the meansfor modifying the coupling comprise means for switching said switch. 9.The system as claimed in claim 6, wherein the device is furtherconfigured to authorize the charging of the power supply battery untilsaid power supply battery is fully charged or until the coupling betweenthe device and the base station is interrupted.
 10. The system asclaimed in claim 6, wherein the device is further configured to detectwhether the power supply battery is fully charged and, if so, to ceaseany and all modification of the coupling via the modifying means. 11.The method as claimed in claim 2, wherein the coupling is modifiedperiodically.